Yes that doc helped me get the eleventy plugin working.
I was trying yesterday a couple online tutorials about creating a more organized sitemap but admittedly I could get none of them to work. Potentially the issue is that none of my pages carry the collection notation that eleventy uses to process a sitemap? Here's one I tried but can't understand why it's not processing, maybe if you are able to better interpret with your experience:
https://11ty.recipes/recipes/add-a-sitemap/
One thing I'm seeing that may be I think relevant to this. It looks like when I use hyperlinks to different pages (the "Page" option rather than the url version) in different parts of the site, it tends to go to the version of the url with the ".html" at the end and leads to a 404 error when the hyperlink is clicked. When I edit the clicked on url in the browser to exclude the ".html", the page is functioning. Probably cleaner to have one of them a functioning version rather than both urls (one without the ".html" and one with), but I accidentally uploaded for indexing a bunch of pages with the ".html" to my google search console. Maybe will need to do some research on how to redirect or try to remove the .html versions of the urls from being indexed.